The California Department of Forestry and Fire Protection has increased staffing and is on high alert because of the increased fire danger from so-called dry thunderstorms, agency spokesman Daniel Berlant said.

Thunderstorms in the forecast for the weekend are expected to produce lightning, but very little rain, Berlant and forecasters said.

Thunderstorms can be a mixed blessing for firefighters because though the precipitation they bring can help douse wildfires, the erratic winds with the storms can also fan the flames.

"The concern always is the storms will bring downdraft winds that push the fire in different directions," Berlant said.

Most of the storms in the forecast for Saturday and Sunday are expected to pack powerful winds, but drop even less rain than a series of thunderstorms that sparked nearly 75 fires last month, Berlant said.

The National Weather Service has issued a "red flag" warning for Saturday and into Sunday evening for a vast section of Northern California, stretching along the Sierra Nevada mountains and west into parts of Mendocino and Lake counties

Because the thunderstorms moving into the area have a "high cloud" base, most of the precipitation produced is expected to evaporate before hitting the ground, said weather service meteorologist Tom Dang.

"The potential is there for explosive fire growth. That's why we have those red flag warnings out," Dang said.

Thunderstorms were expected to make things even more difficult for the 500 firefighters battling the so-called Chips Fire in the Plumas National Forest. That blaze, burning in a rugged area of the forest about 120 miles north of Sacramento, has consumed about 6,000 acres, or nearly 9.5 square miles.

"The terrain is extremely steep and rugged and overgrown. There is no way to get the firefighters in directly to the fire's edge safely," said fire spokesman Larry Ames.

No homes have been destroyed in the blaze, but residents of a handful of homes near the tiny community of Belden have been evacuated, Ames said.

The wildfire is five percent contained, with fire officials expecting to have it contained on Aug. 15.

About 100 miles to the northwest, crews were making progress as they battled a wildfire along Interstate 5 in the Shasta-Trinity National Forest.